The Impacts of Concentrated Ambient Particulates on Heart Rate Variability Rats in Detroit, Michigan and Steubenville, Ohio.

Abstract

Epidemiological studies indicate that inhalation of fine ambient air particulates less than 2.5µm in aerodynamic diameter (PM2.5) are linked to heart rate variability (HRV) and can exacerbate cardiovascular disease in humans. In this study, spontaneously hypertensive (SH) rats were exposed to concentrated ambient particulates (CAPs) to determine if changes in HRV could be associated with individual chemical constituents, or sources of PM2.5. Winter and summer exposures were undertaken in Steubenville, Ohio, and in Detroit, Michigan, for 13 day periods. The observed heart rates of exposed (CAPs) rats and control (AIR) rats were processed to calculate average heart rate (HR) and HRV, (e.g. ln(SDNN), and ln(r-MSSD)). Mixed modeling analyses identified statistically significant differences between AIR and CAPs rats. Specifically, ln(SDNN) was significantly different in the CAPs-exposed rats (Detroit summer study), whereas HR and ln(r-MSSD) were significantly different in CAPs rats (Detroit winter study). In Steubenville HR and ln(SDNN) were significantly different between the CAPs and AIR rats for the summer exposure, whereas the winter study did not find any significant changes in HR or HRV. A sympathetic autonomic response to PM2.5 was indicated during the Detroit summer study. A similar response, increased HR and decreased HRV, was observed in the Steubenville winter study, and was associated with specific PM2.5 constituents, but not PM2.5 mass. Results from Detroit winter and Steubenville summer exposures revealed bidirectional effects on HR and HRV; CAPs constituents were associated with either an increase or a decrease in parameters, which may indicate that various source contributions effect HR and HRV differently. Across the four exposure studies, the concentration of individual PM2.5 constituents had compelling but inconsistent relationships with changes in HRV, and therefore specific constituents cannot easily be attributed to an autonomic response. Positive matrix factorization (PMF) was applied to 30-minute trace element data to identify the major source types, and to calculate their contribution to fine ambient mass. Mixed modeling analysis found that emissions from Iron-Steel manufacturing and Metal Processing facilities were associated with changes in HRV; in Detroit, emissions from Diesel-Motor Vehicles may have enhanced the effect of other attributed sources on HR and HRV.